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Continental drift: effect on climate cycles

  1. Jan 15, 2009 #1
    I'd be interested in any ideas or theories or references on how the location of the continents is thought to affect global warming and cooling cycles. I previously read somewhere that the current position of the continents would cause different net solar heat absorption/reflection than prior locations hundreds of thousands or millions of years ago.

    Don't quote me on this but it may be that currently there are signficiantly greater land masses further from the equator than in past epochs...but I can't remember what the hypothesis was about net absorption/reflection of solar energy relative to earlier periods.
     
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  3. Jan 15, 2009 #2

    mgb_phys

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    I'm not sure that continent movements are really that cyclic.
    Land masses joining and separating have a huge effect on ocean currents and so on local climate.
    N and S America joining directed the gulf stream toward Europe and the separating of Antarctica created the Antarctic circumpolar current that keeps the south pole nice and cold.
     
    Last edited: Jan 15, 2009
  4. Jan 15, 2009 #3

    jim mcnamara

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    It does affect climate in a huge way, and if you view "cycles" as hundreds of millions of years then I guess the answer is 'yes'. The formation of supercontinents (see my definition below) is an example:

    Rodinia was the first supercontinent, then later on at the end of the Triassic, Pangea was the last. That we know about anyway. Ur, Neno and the others mentioned in the literature are excluded by me since they predate multicellular life. Plus, I'm using supercontinent to mean one giant continent made of most all of the continents- not Laurasia or Gondwana which were two continents merged.

    Rodinia has been "blamed" for a long cold period from about ~700 mya to 550 mya.
    This has been referred to as snowball Earth or the 'white Earth hypothesis'
    http://www-eps.harvard.edu/people/faculty/hoffman/snowball_paper.html

    There is newer evidence to refute a complete 'iceball' Earth
    http://www.sciencedaily.com/releases/2007/03/070323104746.htm

    The late Triassic was very warm, possibly the warmest period since multicellular life took hold on Earth- and this hot period this was when Pangea was all together in a large landmass straddling the equator.
    http://www.scotese.com/ltriascl.htm
     
    Last edited: Jan 15, 2009
  5. Jan 15, 2009 #4

    Xnn

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    http://earthobservatory.nasa.gov/IOTD/view.php?id=4073


    It may seem fairly odd, but warming winters actually tends to lead to ice ages as it allows more snow to accumulate than would otherwise. The Laurentide and Euroasian sheets were huge and they only got that way by lots of precipitation.
     
  6. Jan 16, 2009 #5
    I agree with this. It seems logical to suggest that continental drift is also responsible for the mid-Pleistocene transition. This is where the ice ages suddenly became amplified and adherred to the 100-kyr cycle around a million years ago. The restriction of the Indonesian seaway, due to Australia encroaching on Asia, seems a likely possibility to me. It would force westward equatorial currents to join the northward thermohaline circulation. This would then (I'm guessing) increase the strength of the Gulf Stream. A professional report on the situation is Raymo & Lisiecki Report 2007. Source of graph is Maureen Raymo link
     

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    Last edited: Jan 17, 2009
  7. Jan 16, 2009 #6

    Xnn

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    Noticed that there were comments in Raymo's paper regarding Huybers:

    And then concludes:

     
  8. Jan 16, 2009 #7
    I noticed this as well. I'm inclined to think that the Huybers hypothesis regarding the 2 or 3 grouping of obliquity is simply wrong. I'm biased of course, since I think the Earth's orbital 'inclination' is a good fit to explain the 100-kyr cycle. The saw-tooth glacial cycle in a 41-kyr world still needs a full explanation though.
     
  9. Jan 16, 2009 #8
    There are several super continent formations stretching back to the beginning of the non lava stage of the surface.

    The last one was called Gaia IIRC (my mistake it was Pangea) it usually means there is widespread warming and some pretty cataclysmic weather. See albedo effect.

    http://en.wikipedia.org/wiki/Albedo

     
    Last edited: Jan 16, 2009
  10. Jan 16, 2009 #9

    Xnn

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    On the first page is the following paragraph:

    Notice how Raymo is listed more than once!

    So, take your pick; but nobody for the Ithmus of Panama.
     
  11. Jan 16, 2009 #10
    See Milankovich cycles too as the growth of ice sheets effects axial tilt and in turn effects the eccentricity of Earth's orbit which in turn leads to colder conditions or warmer accordingly. It is safe to say that ice sheets cause feedback loops that make everything cooler in front of them thus increasing ice formation, this effects axial tilt which in turn can make it colder still leading to a hypothetical snowball Earth. The effects are exponential at some point.
     
  12. Jan 17, 2009 #11
    The Isthmus of Panama is mentioned a bit earlier on the page of the Raymo & Lisiecki report.
     
  13. Jan 17, 2009 #12

    Xnn

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    Mammo; thanks for pointing that out.


    So, a distinction is made between the initation of NH glaciation and the mid-Pleistocene
    transition (MPT) from a 41K to 100K year cycles. Proposals for the MPT are more subtle.

    Can't say that I really understand shoaling of the thermocline or changes in the North Pacific stratification. However, what impresses me is that all of these proposals may have played a part.
     
  14. Jan 18, 2009 #13
    I agree Xnn. The report is quite difficult to follow in general, I find. Is this where the current scientific investigation has got us? i.e. a bit of a muddle. The simple question as to the asymmetry of the glacial cycles is interesting. Like they say, the orbital insolation is always symmetrical. Where does the asymmetry, saw-tooth graph and rapid deglaciation come from? (I have an idea that I'm working on)
     
  15. Jan 18, 2009 #14

    Xnn

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    From Raymo:

    and

    So, NH ice volumes are postulated to be gradually increasing and as they do, introducing out of phase responses. The SH ice volume is constrained by the geography of Antarctica, where as that is not so in the NH... Possibly, gradually lowering CO2 levels (from more C4 plant life or higher Himilayians?) were allowing NH ice volumes to expand.
     
  16. Jan 21, 2009 #15
    I've thought about this, and the answer seems quite obvious. During deglaciation due to increased insolation, surface meltwater can reach the bottom through glacial fissures. The increased lubrication accelerates the advance of the ice sheet on the American continent due to it's topography. The debris accumulated is more likely to stay near the bottom by the time it is due for iceberg calving. More regular calving would produce smaller bergs with the band of debris located near the base. The bergs would therefore release their IRD relatively quickly, adding to the main deposit just outside the exit of Hudson Bay. Heinrich events are iceberg armadas that occur during glaciation. These are much larger with debris bands often being more centrally located within the berg. Hence the reason why they can traverse the Atlantic before dropping their load of IRD.

    Rapid deglaciation compared to glaciation now makes sense. The topography of the NE American continent allows lubricated glaciers to advance much more quickly to the low-lying Hudson Bay area. Sea-level rise adds to the ability of increased ice melt from continental shelves. This is more a feature of the Antarctic topography, which is currently in a phase of accelerated deglaciation.

    Source of diagram is NOAA
     

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  17. Jan 21, 2009 #16
    The current theory is called plate tectonics and is quite distinct from continental drift, an earlier and dispelled theory. Continents don't drift -they are carried along by plates.

    An important sea is the Artic sea. It is segregated from the other oceans by shallow and narrow connections. During the last Ice Age it was possible to cross the Bering Sea since it was dry.
     
  18. Jan 21, 2009 #17
    The mid ocean ridge secretes new continental crust at different rates. Slower growth can lower the global sea level while faster rates can raise the global sea level. This changes the albedo and total absorption of CO2 while the volcanic activity emits of CO2.
     
  19. Jan 21, 2009 #18
    You mean oceanic crust? The change in albedo is due to what: the water itself (some property of it), the total surface covered by water, or something else?
     
  20. Feb 13, 2009 #19
    Global eustatic sea level change effects the total surface area covered by water. During sea level rise the total surface area covered by water increases and the opposite occurs during sea level fall.

    Position of the continents relative latitude will have an effect on climate. For example, if all the continents were huddled around the polar regions and the tropics were free of continent global temperature would fall. Again, the opposite would ocure when continents are huddled in the tropics witht the polar regions free.
     
  21. Feb 13, 2009 #20
    Here is a short film about the Arctic by NASA from 2003.

    Main article here
    .

    Not only the position of the continents, but the geographic features of the continents, especially mountains. The depth of the oceans effect their circulation and heat transport as well as their ability to regulate the carbon cycle and it's feedback response to albedo flip as the ice sheets erode.

    These changes are gradual, beginning slowly then amplifying as albedo flips, accelerating until the inertia is expended. We are observing a similar phenomenon right now in the Arctic. The more the perennial ice thins the more susceptible it becomes to melting or being blown into the Atlantic or Pacific. That loss of stable perennial ice appears to have reached a tipping point that will likely lead to an open Arctic. Warm Arctic summers are in the near future.
     
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